Soi contact structure(s) and corresponding production method

ABSTRACT

Disclosed are an arrangement and a production method for electrically connecting active semiconductor structures in or on a monocrystalline silicon layer ( 12 ) located on the front face (V) of silicon-on-insulator semiconductor wafers (SOI,  10 ) to the substrate ( 13 ). The electrical connection ( 20 ) is made through an insulator layer ( 11 ). A stack of layers ( 30  to  32, 70  to  72 ) is disposed above the connection piece ( 20 ) on the insulator layer ( 11 ).

The invention relates to SOI structures (silicon on insulator), in which electrical connections are provided between device structures in the upper semiconductor layer insulated from the substrate and the semiconductor substrate, which connections are formed through the insulating layer to the upper semiconductor layer.

An SOI structure consists of a thin semiconductor layer, which is located on a thin oxide layer. The oxide layer is typically formed as a buried oxide (BOX) and is also provided on a semiconductor layer, i.e., generally a silicon layer, that is, the silicon substrate, which usually has a thickness of 300 μm to 800 μm. This substrate serves the purpose of handling the structure. The actual device functions are realized in the semiconductor layer near the surface, similar to usual CMOS processes performed on homogenous silicon wafers.

A significant difference with respect to standard CMOS processes resides in the fact that the devices are dielectrically separated from each other by trenches which extend down to the insulating layer. Hereby, a mutual electrical interaction of the devices is significantly reduced. This dielectric isolation renders the SOI technology also suitable for high voltage applications.

On one hand, it is advantageous when the devices are not coupled to each other via the substrate. Thus, certain non-desired substrate effects may be avoided, such as latch-up, significant reverse currents at elevated temperatures, increased parasitic capacitances at the source/bulk or drain/bulk-pn junctions.

On the other hand, it is advantageous when a substrate connection is provided, for instance, to allow to incorporate into the circuit certain active or passive structures formed in the substrate. In this way, devices may also be integrated that are formed by different techniques not corresponding to the SOI technology. In this case, an electric contact to the substrate would be advantageous. The back side metallization of the substrate, which would be useable for this purpose is, however, not a component of the SOI technology. The corresponding packages do not provide a back side contact and, frequently, the number of pins is not sufficient in the integrated circuits so as to allow a contact to the back side or to root out such a contact.

It is the object of the invention to provide an electrical connection of SOI device structures within an active silicon layer to the substrate, while circumventing or avoiding a back side metallization of the substrate. Thereby, the degree of integration of circuits is to be increased. Also, devices not corresponding to the SOI technology are to be taken into consideration.

The solution of the present invention is described in the characterizing portion of claims 1 or 7, or is defined by the features of claims 11 or 20. Further embodiments of the invention are defined in the dependent claims.

In this way, a via thus provides a connection of active structures located on the front side to the substrate. The connection may be provided as a single or a multiple connection, such as in the claimed layer stack, so that different device groups on the front side may be individually connected to the substrate.

Also, a connection of device structures from the front side with doped regions in the substrate is contemplated.

Formed on the insulating layer of the SOI wafer is at least one layer sequence consisting of respective two layers.

From these layers, a first passivation layer having an opening is located above the metal filling, above which a second layer is located as a metallization layer that is conductively connected to the metal filing and that provides electrical contact, that is, a conductive structure, to the substrate so as to contact or conductively connect to the substrate structures that are prepared on the front side of the SOI.

A multiple repetition results in a sequence of a respective passivation layer having an opening above the area of the metal filling, and of a respective metallization layer located above the passivation layer within the area of the metal filling. An electrical contact is established between the substrate and the structures that are prepared from the front side of the wafer, so that the stack comprises different conductive height layers of several alternating metal and passivation layers, wherein the height layers have a different spacing with respect to the insulating layer.

Exemplary embodiments explain and complete the invention, wherein identical reference numerals denote identical elements.

FIG. 1 illustrates a first embodiment in which a contact to a substrate is established via a layer stack.

FIG. 2 illustrates the embodiment of FIG. 1 with explanatory reference numbers.

FIG. 3 depicts a further embodiment with an additionally indicated separate lateral connection on the substrate above the insulating layer 11, wherein the connection originates from the first metallization 70. The active structures on the front side are schematically illustrated at 40 and 50, which are in FIG. 1 not explicitly shown so as to clearly illustrate a substrate contact.

For a more detailed explanation of the invention, FIG. 1 is provided, schematically showing the contacting of the substrate via a layer stack.

In this way, the via provides a connection of the active structures on the front side to the substrate. The connection may be provided as a single or a multiple connection, as is the case in the stack shown in FIG. 1, so that different device groups on the front side may be individually connected to the substrate. Also, the connection with the substrate of device structures on the front side and having doped regions is feasible.

With the reference numerals provided in FIG. 1, this figure is self-explanatory and no further explanation is necessary.

A contact is formed at the interfaces between the metal of the via and the substrate. This contact may represent an ohmic contact or a Schottky contact. Both types of contacts are of technological relevance and may be specifically implemented.

The contacting of the substrate according to FIG. 1 is also illustrated in FIG. 3. The arrangement is identical. The additional reference numerals are provided for a detailed explanation of the layer stack, which is provided at each via 19, 20. The contacting of the substrate is obtained in the same way as in FIG. 1, that is, by the layer stack 80 comprised of a plurality of layers, which includes in this example six layers. The via 20 is a metallic filling of an opening or a through hole 19 in the insulating layer 11 that, in turn, is a component of an SOI wafer 10. The substrate 13 bears the insulator 11, for instance, in the form of a BOX layer. Located above the insulator 11 is a semiconductor layer 12, which is already illustrated as a patterned layer and which is depicted in the left and right peripheral area as a patterned residual layer 12′ and 12″ for receiving, at least partially, active devices. These devices are symbolically indicated at 40 and 50 and are located at the left side and the right side of the layer stack 80, which is located in an area that lacks the single crystalline semiconductor layer 12. This area is indicated as 12 a, wherein the entire single crystalline semiconductor layer 12 results in the residual layers 12′ and 12″ by patterning this area, i.e., the area 12 a, lacking the semiconductor layer.

The via 19 in the form of, for instance, an etched throughhole, is filled with a metal material for forming a metal layer (or a metal plug), which is substantially flush with the insulating layer on the upper side and lower side or which lands on the substrate layer 13 at the lower side.

In this way, the via represents a connection of active structures 40, 50 on the upper side (front side V) of the SOI wafer to the substrate 13 that has a back side R.

This via may be formed as an individual one or as multiple vias, as is shown for the stack in FIG. 1. In this way, different device groups on the front side may individually be connected to the substrate. Different devices (or device groups) may also be connected to the same via or conductive connection 20 so as to conductively connect a plurality of devices with the same substrate location at the same via 19/20. Doped regions, which are not explicitly shown, may be provided on the surface of the substrate in the via opening 19. If a doped region is not provided, a Schottky contact 13 c is created, as is illustrated in FIG. 2. With a doped region having a p- or an n-doping, an ohmic contact to the substrate 13 is formed. This boundary area is referred to as “interface” between the metal of the via and the substrate.

The layer sequence 30 to 32, i.e., interleafed therein the layers 70 to 72, will be explained below.

In one manufacturing method, the stack structure of the layers according to FIG. 2 is obtained. The substrate contact 20 is formed to the front side and is there provided as a stack so as to allow to metallically contact the stack in different levels at different heights or spacing with respect to the insulating layer 11. These different levels are each spaced apart by a thickness of a passivation layer 70, 71, 72, which are provided in an alternating fashion within the stack and which comprise a via opening through which the metallic conductor 20 is established by the metallization layers 70, 71, 72 so that a central or inner via through the stack is formed, which is located above the via opening 19 and which is completely filled in a metallic conductive manner.

At locations that are not covered by the active semiconductor layer 12, i.e., the trench 12 a, the insulating layer is provided with the via opening 19, particularly by an etch process, wherein the via opening extends to the substrate 13. A plurality of openings may be etched substantially simultaneously in a spaced apart relationship.

A metal via 20 is formed by filling in the respective via opening 19. The metal via is substantially flush with the insulating layer.

Above the metal via 20 a worked through passivation layer 30 is deposited as a first passivation that has a lateral extension and that is formed on the insulator 11. In a further process step, a metal layer 70 is formed, which reaches through the opened passivation layer at the worked through portion and that electrically contacts the metal layer 20 in the via opening, as is shown at 70 a. The contact area 20 a exhibits a recess, which substantially corresponds to the shape or extension of the worked through portion extending through the passivation layer 30.

If necessary, the first metal layer 70 may be patterned so as to provide the electrical contact within the area of the device structures. This is illustrated by means of the lateral conductor 70 a, originating from the first metallization 70, in FIG. 3, representing a further embodiment. The laterally extending conductor 70 a connects to the structure 40 prepared in the active semiconductor layer 12′. This lateral connection extends on the first level (height level) above the surface of the insulating level 11.

A further passivation layer 31 is formed on the metallization 70 and is also opened as is the case for the first passivation layer 30.

The described sequence of layer pairs formed of a passivation and a metallization may be repeated several times, for instance, the second passivation 31 and the second metallization 71. A third passivation 32 and a third metallization 72 may follow, as is illustrated in FIG. 2.

The passivation is worked through within the area above the metallic via 20 in order to form a central or inner core of metallic material for the conductive connection even of the uppermost metallization layer 72 to the substrate 13, that is, to the ohmic or Schottky contact 13 c.

In the lateral direction, the further away the passivation layers are spaced from the insulating layer 11, the more they are reduced. The stack tapers in the upward direction, as is evident from the section of FIGS. 1 to 3.

In FIG. 3, in a further embodiment, there is shown an assumed metal conductor 72 b at the third level, which extends to a further structure 50 prepared in the active semiconductor layer 12″ and there the conductor establishes an electric contact similar to the conductor 70 a laterally extending to provide contact to the first structure 40 prepared on the closed height level.

The various electric conductors are connected via the stacked metallization and from different levels so as to commonly electrically contact them with the substrate 13 by means of the via 19/20.

In a plan view, the described structures and, in particular, the stack structure 80, is not provided in a circular form in its outer extension but, instead, is preferably of rectangular or square shape.

A plurality of the described stack structures may be arranged within areas, which are not covered by the active semiconductor layer, and which correspond to the “trench” 12 a. 

1. Substrate contacts extending to the front side of silicon-on-insulator semiconductor wafers (SOI), which are comprised of a thin monocrystalline silicon layer located on a thin insulating layer, wherein this double layer is carried by a monocrystalline semiconductor substrate, characterized in that the insulating layer comprises through holes in areas lacking the monocrystalline semiconductor layer, said through holes extends to the substrate and being filled with metal, and at least one layer stack is located on the insulating layer, comprised of two respective layers, wherein the first layer represents a passivation layer having an opening above the area of the metal filling, above which the second metallization layer is located, that is connected to the metal filling and that provides the electric contact between the substrate and structures prepared on the wafer front side.
 2. The substrate contacts extending to the front side according to claim 1, characterized in that the insulating layer is a silicon dioxide layer.
 3. The substrate contacts extending to the front side according to claims 1 and 2, characterized in that the passivation layer is a silicon nitride layer.
 4. The substrate contacts extending to the front side according to claim 3, characterized in that the substrate is comprised of a highly doped monocrystalline silicon wafer.
 5. The substrate contacts extending to the front side according to claim 1 characterized in that the metal filling forms an ohmic contact with the substrate.
 6. The substrate contacts extending to the front side according to claim 1, characterized in that the metal filling forms a Schottky contact with the substrate.
 7. A method of forming substrate contacts extending to the front side of silicon-on-insulator (SOI) semiconductor wafers including the following main method steps: etching a through hole into the insulating layer (oxide layer) down to the substrate at locations, which are not covered by the active semiconductor layer; forming a metal via by filling the through hole with a metal layer that is bordered by the insulating layer; forming a passivation layer that is worked through at the metal via; depositing a further metal layer and if necessary patterning the same within the area of the device structures, said metal layer providing the electric contact to the structures prepared on the front side in the active semiconductor layer; forming a further passivation layer.
 8. The method of claim 7, wherein the sequence for forming a passivation layer, having an opening above the area of the metal filling and a metallization layer located above this passivation layer and above the area of the metal filling and providing the electric contact between the substrate and structures prepared on the wafer front side, is repeated multiple times so as to form a stack of several alternating metal and passivation layers.
 9. The method of claim 7 characterized in that the conditions at the interface metal/substrate are selected such that an ohmic contact to the substrate is formed.
 10. The method of claim 7 characterized in that the conditions at the interface metal/substrate are selected such that a Schottky contact to the substrate is formed.
 11. A silicon-on-insulator semiconductor wafer having at least one substrate contact (13 c, 20) extending to the front side (V), wherein said wafer (10) has a patterned monocrystalline semiconductor layer (12; 12′, 12″) located on an insulating layer (11) wherein the layers are carried by a monocrystalline semiconductor substrate (13), wherein (i) the insulating layer (11) comprises worked through portions (19) in areas not covered by the monocrystalline semiconductor layer, said worked through portions extending to the substrate (13) and being filled (20) with a metal, (ii) at least one layer sequence is formed on said insulating layer, the layer sequence being comprised of two respective layers (30, 70; 31, 71); (iii) from the layers a first one is a passivation layer (30) having an opening above the metal filling (20), above which is located a second layer as a metallization layer (70), which is conductively connected to the metal filling and which provides electrical contact or a conductive structure to the substrate (13) so as to contact or conductively connect structures (40, 50) prepared on the front side (V) with the substrate.
 12. The semiconductor wafer of claim 11, wherein the insulating layer is a silicon dioxide layer.
 13. The semiconductor wafer of claim 11, wherein the passivation layer (30) is one of a silicon nitride layer and a plasma nitride layer.
 14. The semiconductor wafer of claim 13, wherein the substrate is comprised of highly doped monocrystalline silicon.
 15. The semiconductor wafer according to claim 11, wherein the metal filling (20) forms an ohmic contact with said substrate.
 16. The semiconductor wafer according to claim 11, wherein the metal filling (20) forms a Schottky contact (13 c) with said substrate. 16a. (canceled) 16b. (canceled) 16c. (canceled) 16d. (canceled)
 17. A method for forming substrate contacts extending to a front side on a silicon-on-insulator (SOI) semiconductor wafer, comprising the following steps: forming at least one via opening in an insulating layer (11) at locations that lack an active semiconductor layer (12, 12′, 12″), said via opening extending to the substrate; forming a metal via (20) by filling the via opening with metal that is substantially bordered by said insulating layer; forming a first passivation layer (30) at the metal via (20), which layer is worked through or intercepted; forming a metal layer (70) on said passivation layer (30); forming a further passivation layer (31) on said metal layer (70).
 18. The method of claim 17, wherein the sequence of the manufacturing of the first passivation layer having an opening above the area of the metal filling and of a metallization layer located thereabove, which is located above the first passivation layer and within the area of the metal filling for providing electrical contact between the substrate and structures prepared from the front side of the wafer is repeated multiple times so as to form a stack of several alternating metal and passivation layers (30, 70; 31, 71; 32, 72).
 19. The method of claim 17, wherein the conditions at the interface between metal (20) and the substrate are selected such that an ohmic contact to the substrate is formed.
 20. The method of claim 17, wherein the conditions at the interface between metal (20) and the substrate are selected such that a Schottky contact (13 c) to the substrate is formed.
 21. The method of claim 17, wherein the at least one opening (19) is formed by etching.
 22. The method of claim 17, wherein the metal layer (70, 71) is patterned in the area of the device structures in order to provide electrical contact to structures prepared on the front side in the active semiconductor layer.
 23. The method of claim 17, wherein a further metal layer (71) is formed on the passivation layer (31).
 24. The method of claim 17, wherein a plurality of via openings and a plurality of metal fillings (20) is provided, each of which is provided with a layer sequence of a plurality of pairs of passivation layers and metal layers (30, 70).
 25. The method of claim 17, wherein a layer (73) of the layer sequence (80) being located more distantly from the insulating layer (11) has a reduced lateral extension compared to a layer (30) of the layer sequence (80) that is located more closely to the insulating layer (11).
 26. The method of claim 17, wherein the layers are not circular in shape at the perimeter thereof.
 27. The method of claim 17, wherein at least two devices (40, 50) formed on at least two non-identical levels (70, 71, 72) of the layer stack (80) are electrically conductively connected (70 a, 72 b) with metallization layers (70, 72) of the stack that are located on at least two non-identical levels by means of the same metal filling (20).
 28. The semiconductor wafer of claim 11, wherein the layer sequence (80) is provided at least two times as a stack.
 29. The semiconductor wafer of claim 11, wherein the layer sequence is provided at least three times for forming a layer stack having a metallic vertical core (20, 70 a, 71 a, 72 a).
 30. The semiconductor wafer of claim 11, wherein a geometry of the perimeter of the layer sequence has a polygonal configuration.
 31. The semiconductor wafer of claim 11, wherein the layers of a respective layer sequence are substantially planar. 